FIGS. 1, 2A, 2B, and 2C show a conventional electronics device unit 1. The electronics device unit 1 includes a rectangular circuit board 2 having an upper surface on which CPUs and the like are mounted. The electronics device unit 1 further includes a cover member 13. The cover member 13 includes a ceiling plate part 13a, and side plate parts 13b and 13c at both sides of the cover member 13 to form a tunnel 12. The electronics device unit 1 further includes motor fan units 14-1 and 14-2 that send air into the tunnel 12, and motor fan units 15-1 and 15-2 that discharge the air existing in the tunnel 12. The air flows in the tunnel 12 that is an air flow passage in the direction indicated by the arrows 16 to provide forced draft cooling to the CPUs and the like. As for the air flow, the Y2 direction indicates an upstream side, and the Y1 direction indicates a downstream side. The Y2-Y1 directions are longitudinal directions of the circuit board 2 and the electronics device unit 1, and the X1-X2 directions are width directions of the circuit board 2 and the electronics device unit 1. Six CPUs 20-1 through 20-6, one system control element 21, two memory control elements 22-1 and 22-2, one clock control element 23, a plurality of memory cards 24, and the like are mounted on the upper surface of the circuit board 2. The memory cards 24 are arranged with the memory cards 24 standing, and constitute two memory card groups 25-1 and 25-2. A plurality of connectors 26 are arranged along one side of the circuit board 2. Heat sinks 30-1 through 30-6 are installed on upper surfaces of the CPUs 20-1 through 20-6, respectively. Similarly, a heat sink 31 is installed on an upper surface of the system control element 21, heat sinks 32-1 and 32-2 are installed on upper surfaces of the memory control elements 22-1 and 22-2, respectively, and a heat sink 33 is installed on an upper surface of the clock control element 23.
The electronics device unit 1 is electrically connected to other electronics device units via a back panel board or the like (not shown in the drawings) by the connectors 26 so as to configure a computer main body.
Out of the elements mounted on the circuit board 2, the CPUs 20-1 through 20-6 generate a large amount of heat at the time of the operation, so that targets for forced draft cooling are the CPUs 20-1 through 20-6.
The CPUs 20-1 through 20-6, the system control element 21, the memory control elements 22-1 and 22-2, the clock control element 23, and the memory card groups 25-1 and 25-2 are uniformly dispersed on the circuit board 2. The Y1-Y2 directions correspond to a row, and the X1-X2 directions correspond to a column. That is, the CPUs 20-1 through 20-6 are arranged in two rows and three columns.
FIG. 3A is a cross-sectional view taken along the line IIIA—IIIA of FIG. 2A, i.e., a section orthogonal to the air flow at the positions of the CPUs 20-1 and 20-2 that are located at the upstream side. FIG. 3B is a cross-sectional view taken along the line IIIB—IIIB of FIG. 2A, i.e., a section orthogonal to the air flow at the positions of the CPUs 20-5 and 20-6 that are located at the downstream side. In FIGS. 3A and 3B, the hatched parts indicate the heat sinks 30-1, 30-2, 30-5, and 30-6 that occupy a certain part of the tunnel 12 and that have sectional areas S30-1, S30-2, S30-5, and S30-6, respectively. The areas S30-1, S30-2, S30-5, and S30-6 have the same size of the area. S12 indicates the sectional area of the tunnel 12. S40 indicates the sectional area of a clearance 40 between the cover member 13 and the heat sinks 30-1 and 30-2. That is, S40=S12−(S30-1+S30-2). S41 indicates the sectional area of a clearance 40 between the cover member 13 and the heat sinks 30-5 and 30-6. That is, S41=S12−(S30-5+S30-6).
A ratio S40/S12 (S41/S12) of the clearance area 40 (the clearance area 41) to the sectional area S12 of the tunnel 12 is defined as a clearance ratio U.
As understood from FIGS. 3A and 3B, an air flow passable sectional clearance ratio U2 (S41/S12) at the downstream side is the same as an air flow passable sectional clearance ratio U1 (S40/S12) at the upstream side. That is, U1/U2=1. In addition, an air flow passable sectional clearance ratio at the midstream is also the same as the air flow passable sectional clearance ratio at the upstream side.
As shown in FIG. 2B, a distance in the air flow direction between the CPUs 20-1 and 20-2 at the upstream part and the CPUs 20-3 and 20-4 at the midstream part is equal to a distance in the air flow direction between the CPUs 20-3 and 20-4 at the midstream part and the CPUs 20-5 and 20-6 at the downstream part, and is “a”. This distance “a” is about 15 mm.
Next, forced draft cooling of the CPUs 20-1 through 20-6 will be described.
The air flow passable sectional clearance ratios take the same value at all of the upstream part, the midstream part, and the downstream part of the air flow, so that the air flow in the tunnel 12 is uniform.
FIG. 4 shows a result of testing. The test was performed under the condition in which a calorific value (heat release value) of each CPU 20-1 through 20-6 was 100W, a temperature of intake air was 25° C., and a wind speed of the air flowing into the tunnel 12 was 2 m/s. In FIG. 4, the vertical axis indicates the distance in the Y1 direction from the motor fan units 14-1 and 14-2, and the horizontal axis indicates the temperature. While the air flows, the air transfers heat from the heat sink 30-1 and so forth. In other words, while the air flows, the air is heated by the heat sink 30-1 and so forth, and the temperature of the air is raised. The cooling ability of the air (rate of heat transfer) is gradually lowered as the air advances to the downstream side.
As shown by the (curved) line of FIG. 4 and in FIG. 2B, when the air passes through the heat sinks 30-1 and 30-2 at the upstream part, the temperature of the air is raised to 40° C., and the air passes through the heat sinks 30-3 and 30-4 at the midstream part, and flows into the heat sinks 30-5 and 30-6 at the downstream part. At this time the air flows into the heat sinks 30-5 and 30-6, the temperature of the air already reaches 55° C. After the air passes through the heat sinks 30-5 and 30-6 at the downstream part, the temperature of the air is raised to 70° C.
Accordingly, as indicated by the points O1, O2, and O3 of FIG. 4, the temperature of the CPUs 20-1 and 20-2 at the upstream part does not exceed 50° C., the temperature of the CPUs 20-3 and 20-4 at the midstream part does not exceed 70° C., but the temperature of the CPUs 20-5 and 20-6 at the downstream part reaches 90° C. Therefore, there is a possibility that the cooling of the CPUs 20-5 and 20-6 at the downstream part is not sufficient.
In the future, accompanying the improvement of the server, it is expected that the amount of heat generated by each of the CPUs 20-1 through 20-6 will be further increased. In this case, a rate of the temperature rise of the CPUs 20-5 and 20-6 at the downstream part will be greater than a rate of the temperature rise of the CPUs 20-1 and 20-2 at the upstream part and the CPUs 20-3 and 20-4 at the midstream part. The cooling of the CPUs 20-5 and 20-6 at the downstream part will become a serious problem. A size of a space part 50 located directly upstream of the heat sinks 30-5 and 30-6 at the downstream part is the same as a size of a space part 51 located directly upstream of the heat sinks 30-3 and 30-4 at the midstream part. The distances “a” of the space parts 50 and 51 are about narrow 15 mm. Therefore, an amount of the air that flows into the space part 50 from the Y1 direction side and the Y2 direction side is not large. This also contributes to a difficulty in efficiently cooling the CPUs 20-5 and 20-6 at the downstream part.